1. Field of the Invention
The present invention relates to a vehicle which is constructed to transmit a torque of a driving force source through a transmission to wheels and, more particularly, to a hybrid vehicle in which a torque of another driving force source can be inputted to a torque transmitting route between one driving force source and the wheels.
2. Related Art
As well known in the art, an internal combustion engine outputs a kinetic energy by mixing and burning air and a fuel. As a result, the internal combustion engine discharges exhaust gases inevitably. The constituents and amount of the exhaust gases depend a running state of the internal combustion engine. According to the general tendency, not only the clarification of the exhaust gases but also the fuel economy are liable to become low at a high-load running time when the throttle opening is large. In recent years, on the contrary, a demand for the clarification of the exhaust gases of the vehicle having the internal combustion engine mounted thereon grows higher and higher. In order to satisfy this demand, there has been developed a hybrid vehicle which has an engine, an electric motor and a transmission mounted thereon. In this hybrid vehicle, the running state is judged on the basis of the accelerator opening and the vehicle speed to drive/stop the engine and the electric motor and to control a gear ratio of the transmission in accordance with the result of judgment.
One example of the hybrid vehicle thus having the engine, the electric motor and the transmission mounted thereon is disclosed in Japanese Patent Laid-Open No. 9-37411. According to this disclosure, the vehicle is constructed such that the torque of the engine is inputted through a planetary gear mechanism to a continuously variable transmission. On the other hand, the output side of the continuously variable transmission is connected to transmit the torque to the wheels. The continuously variable transmission is provided with an input rotary member, an output rotary member and a disc. These input rotary member and output rotary member are formed to have arcuate faces. Moreover, the disc is in contact with the arcuate face of the input rotary member and the arcuate face of the output rotary member. Th is continuously variable transmission is the so-called xe2x80x9ctoroidal type continuously variable transmissionxe2x80x9d. On the other hand, the output rotary member and the wheels are so connected as to transmit the torque.
The planetary gear mechanism includes a sun gear, a ring gear, and a carrier holding a pinion gear meshing with the sun gear and the ring gear. Moreover, the engine and the ring gear are connected in the torque transmittable manner, and the carrier and the input rotary member are connected in the torque transmittable manner. On the other hand, the sun gear and the electric motor are connected in the torque transmittable manner. Of the rotary element s of the planetary gear mechanism, moreover, the ring gear to which the torque of the engine is inputted acts as an input element. When this ring gear rotates, the sun gear to which the torque of the electric motor is inputted acts as a reaction element so that its torque is outputted from the carrier. The torque thus outputted from the carrier is inputted to the continuously variable transmission. In this continuously variable transmission, the gear ratio is set on the basis of a ratio between a radius of a contact point between the disc and the input rotary member and a radius of a contact point between the disc and the output rotary member. Therefore, the torque, as inputted to the continuously variable transmission, is decelerated or accelerated according to the gear ratio and transmitted to the wheels.
In the hybrid vehicle thus described, however, the high torque, as decelerated or synthesized by the planetary gear mechanism, is inputted to the continuously variable transmission. As a result, a slippage may occur between the torque transmitting members for transmitting the torque between the input side and the output side of the continuously variable transmission, that is, between input rotary member and the output rotary member, and the disc, to lower the transmission efficiency of the motive power. In order to prevent this slippage, on the other hand, the input/output members and the disc have to be brought into contact by a stronger force. The rise in this contact pressure may lower the transmission efficiency of the motive power.
A main object of the invention is to improve a transmission efficiency of a motive power in a transmission and to make the system compact.
A specific object of the invention is to improve a transmission efficiency of a motive power in a hybrid vehicle including at least two driving force sources and a continuously variable transmission.
Another object of the invention is to make compact an entire construction of a system including a mechanism for switching a drive state into a backward run.
According to a feature of the invention, there is provided a hybrid vehicle which comprises: a first driving force source; a transmission for transmitting the torque of the first driving force source therethrough to wheels; a second driving force source; and a torque transmitting route interposed between the first driving force source and the wheels for inputting the torque of the second driving force source. The hybrid vehicle further comprises a torque adding route for synthesizing the torque outputted from the transmission and the torque transmitted from the second driving force source, to output the synthesized torque to an output member.
The first driving force source can be constructed of an internal combustion engine, and the second driving force source can be constructed of an electric motor or a motor/generator. Moreover, the transmission can be constructed of a continuously variable transmission.
The torque of the second driving force source is added on the output side of the transmission to the output torque of the transmission. Therefore, the torque to be applied to the transmission is one to be transmitted from the first driving force source, i.e., a relatively low torque so that the transmission efficiency of the motive power in the transmission is improved.
Especially if the transmission is a belt type continuously variable transmission, the slippage of the belt is suppressed because of the low transmitted torque, and the transmission efficiency of the motive power is improved because a tension to be applied to the belt is lowered.
The torque adding route in the hybrid vehicle of the invention can be constructed of a Ravigneaux type planetary gear mechanism, one set of single-pinion type planetary gear mechanisms or a plurality of sets of planetary gear mechanisms.
When the torque adding route is constructed of the planetary gear mechanism, at least two high and low gear ratios can be set by the planetary gear mechanism. With this construction, it is possible to increase/decrease the torque to be outputted by the second driving force source. On the other hand, it is possible to change the RPM (i.e., revolutions per minute) of the case in which the second driving force source is forcibly driven.
When the torque adding route is constructed of the planetary gear mechanism, moreover, it is possible to give a forward/backward switching function to reverse and output the torque inputted. With this construction, the system can be made compact as a whole.
The above and further objects and novel features of the invention will more fully appear from the following detailed description when the same is read with reference to the accompanying drawings. It is to be expressly understood, however, that the drawings are for the purpose of illustrations only and are not intended as a definition of the limits of the invention.